ENERGY PRINCIPLE OF THE INDENTATION-INDUCED INELASTIC SURFACE DEFORMATION AND HARDNESS OF BRITTLE MATERIALS

Energy-based considerations on the inelastic surface deformation of brittle materials are conducted. The hysteresis loop energy U(r) which is dissipated during the indentation loading-unloading cycle is related to the true hardness H, apparent hardness H, and the work-of-indentation LAMBDA1. The true hardness has its energy-derived meaning of the irreversible energy consumption to create a unit volume of the indentation impression of ideally plastic materials. The relationships between U(r) and the three-half power of indentation load P3/2, and between U(r) and the volume of the indentation impression V1 are used to separate the plastic contribution from the complicated plastic/elastic surface deformation processes in indentation hardness tests. The linear relationship of U(r) vs P3/2 provides an important experimental technique for determining the true hardness H of brittle materials. The linear relationship of U(r) vs V1 is available to the experimental determination of LAMBDA1. The mechanical and physical meanings of the conventional Vickers indentation hardness of brittle materials are also addressed in relation to H, H and LAMBDA1.